1. Field of the Invention
This invention relates to a vertical sharpness adjustment device which provides a video signal (brightness signal) with a sharpness adjustment in vertical direction on a TV (television) screen and a TV receiver equipped with it, specifically to a vertical sharpness adjustment device which provides a vertical sharpness adjustment best suitable for viewer's requirement and a TV receiver equipped with it.
2. Description of the Related Art
A sharpness adjustment has been known as one of functions a TV receiver is provided with. The sharpness adjustment is to enhance a contour of a picture in horizontal direction. When a contour of an object is enhanced, the object looks crisp. The object looks crispier to a viewer compared with a case in which the contour is not enhanced. In addition to the sharpness adjustment, the TV receiver is provided with following adjustment functions.                Brightness: an adjustment to brightness        Contrast: an adjustment to difference in brightness between black and white        Color: an adjustment to depth of a color        Tint: an adjustment to a hue        
In general, these parameters can be adjusted by a viewer to his/her requirements. The adjustments are made either with a knob on the TV receiver itself or with a remote controller referring to adjustment values displayed on the TV screen.
FIG. 2 shows an example of display of the adjustment values displayed on the TV screen with the remote controller. Five parameters, i.e. BRIGHTNESS, CONTRAST, SHARP, COLOR and TINT, are displayed from top to bottom in FIG. 2. The display means that the five parameters, i.e. BRIGHTNESS, CONTRAST, SHARP, COLOR and TINT, are adjustable to the viewer's requirements with the TV receiver.
It also means that BRIGHTNESS is currently under adjustment and a degree of BRIGHTNESS is 32. The viewer can set the degree of BRIGHTNESS to an arbitrary value within a range of 0–63, for example. In this way, the viewer can choose best suitable values accordingly to his/her likings and/or reception conditions (intensity of airwaves and so on), regarding the five parameters mentioned above.
The sharpness adjustment function of a TV receiver is described in a following patent document.                Kokai No. 10-93842.        
However, the viewer has not been able to adjust a vertical sharpness which enhances a contour of a picture in vertical direction with a conventional TV receiver. The vertical sharpness adjustment is to enhance the contour in vertical direction when the brightness of a video signal changes from black to white or from white to black, over a period of around 1H (one horizontal period). In this case also, an object looks crispier compared with a case in which the contour is not enhanced.
The vertical sharpness adjustment has a positive effect to make the object look crispier on the one hand, but also has a negative effect to increase noise on the screen on the other hand. For this reason, performing the vertical sharpness adjustment in a weak airwave area or the like would result in severe noise on the screen, giving the opposite effect to what was intended.